Be a shame to have to start all over again with a new pen. I like to soak all day in pen flush if things are really blocked up. Then after everything is softened up, I blow it out using the same flush and my modified ear syringes. They are cheap. You can buy them from Goulet or your local drug store. They use them on babies. The size I've cut these three allows me to get into the back end of a section, fit over the front, covering the nib and section, the middle size fits perfectly over a pelikan nib unit. I've used them on everything from Montblanc to Jinhao, they work great.
I'm going to go out on a limb here. Wondering aloud if you don't have an ink interaction going on. Not all inks are compatable. Sometimes changing to what is normally a perfectly good ink can cause the symptoms you are having. It's my personal belief that some feeds especially ebony will absorb some ink into the material. You may have cleaned the ink channels, but there is still stuff imbedded in the feed material itself. I've seen several older threads where people talk about seasoning the feed of a new pen with Waterman Florida Blue.
I recommend soaking in a 1:10 solution of water and no suds Amonia, with just a couple drops of plain dawn dish soup.(without fancy additives, like antibacterial)Soak it all day or night, then blow it out with the ear syringes full of the flush solution. Repeat the process over again until you get a free flow of liquid through the nib and section. Also hold the nib under a water faucet with a slow steady stream of water. Let the water hit the ink groove and breather hole on top then turn it over. Let the water gently hit the feed, but especially the "wings" of the metal nib so that the water gets up in between the feed and nib. You're trying to get any dried ink or crystaline material that can result from inks that don't play well together. You don't need a lot of pressure for this, and make sure you have the strainer In the sink drain. If you drop that nib by mistake, I guarantee it is going down the drain.
I would also try dipping the top of a tooth pick in dish soap and pushing it up into the converter full of ink. Swish it around, and pull out. Won't hurt the pen, but if you are having a surface tension issue, it may solve it.
I've thrown some ideas out here. If something rings true to you, give it a try and let us know. We are all learning through you now.
Hope this all helps.
I apologize for any weird words. I think I caught them all. My iPad is making up words again..agghhhh!!